The invention relates to conveyor lubricants and lubricant compositions, and to methods of use, for example, to treat or lubricate a container(s) and conveyor surfaces or system for containers. The invention also relates to containers and conveyor surface or system treated with a lubricant or lubricant composition. The container is, for example, a food or beverage container.
Containers are receptacles in which materials are or will be held or carried. Containers are commonly used in the food or beverage industry to hold food or beverages. Often lubricants are used in conveying systems for containers, to ensure the appropriate movement of containers on the conveyor.
In the commercial distribution of many products, including most beverages, the products are packaged in containers of varying sizes. The containers can be made of paper, metal or plastic, in the form of cartons, cans, bottles, Tetra Pak(trademark) packages, waxed carton packs, and other forms of containers. In most packaging operations, the containers are moved along conveying systems, usually in an upright position, with the opening of the container facing vertically up or down. The containers are moved from station to station, where various operations, such as filling, capping, labeling, sealing, and the like, are performed.
Containers, in addition to their many possible formats and constructions, may comprise many different types of materials, such as metals, glasses, ceramics, papers, treated papers, waxed papers, composites, layered structures, and polymeric materials. Any desired polymeric material can be used, such as polyolefins, including polyethylene, polypropylene, polystyrene, and mixtures thereof, polyesters such as polyethylene terephthalate (PET or PETE) and polyethylene naphthalate (PEN) and mixtures thereof, polyamides, polycarbonates, and the like.
Lubricating solutions are often used on conveying systems during the filling of containers with, for example, beverages. There are a number of different requirements that are desirable for such lubricants. For example, the lubricant should provide an acceptable level of lubricity for the system. It is also desirable that the lubricant have a viscosity which allows it to be applied by conventional pumping and/or application apparatus, such as by spraying, roll coating, wet bed coating, and the like, commonly used in the industry.
In the beverage industry, it is also important that the lubricant be compatible with the beverage so that it does not form solid deposits when it accidentally contacts spilled beverages on the conveyor system. This is important since the formation of deposits on the conveyor system may change the lubricity of the system and could require shutdown of the equipment to facilitate cleaning.
It is also important that the lubricant can be cleaned easily. The container and/or the conveyor system may need to be cleaned. Since water is often in the cleaning solution, ideally the lubricant has some water-soluble properties.
Currently, containers, including polyethylene terephthalate (PET) bottles, and conveying systems for containers are often contacted with a volume of a dilute aqueous lubricant to provide lubricity to the container so that it can more easily travel down the conveyor system. Many currently used aqueous-based lubricants are disadvantageous because they are incompatible with many beverage containers, such as PET and other polyalkylene terephthalate containers, and may promote stress cracking of the PET bottles.
Furthermore, aqueous based lubricants are in general often disadvantageous because of the large amounts of water used, the need to use a wet work environment, the increased microbial growth associated with such water-based systems, and their high coefficient of friction. Moreover, most aqueous-based lubricants are incompatible with beverages.
Flooding a conveyor surface with a substantial proportion of aqueous lubricant typically occurs on food container filling or beverage bottling lines. Sufficient lubricant is used such that the lubricant is not retained entirely by the surface of the conveyor but tends to flow from the surface of the container, drip onto a conveyor support members and the surrounding environmental area around the conveyors. Further, sufficient amounts of lubricant are applied to the conveyor and other mechanisms of the plant under such conditions that a substantial foam layer of lubricant can form on the surface of the conveyor. As much as one inch (about 2.5 cm or more) thick of lubricant foam can contact a substantial portion of the base of a food container such as polyethylene terephthalate beverage bottle. We have found that current methods of lubricating such containers are wasteful of the lubricant material since a substantial proportion of the materials is lost as it leaves the container surface. Further, substantial proportions of the lubricant remain on the container and are carried from the conveyor as the food packaging or beverage-bottling operations are continued. A substantial need exists for approved methods that waste little or no lubricant during packaging or bottling operations.
The tendency of polyester beverage containers to crack or craze is promoted by the presence of a number of common lubricating materials in contact with a substantial proportion of the surface of a polyester beverage container under pressure. The stress arises during manufacture of the polyester bottle from a preform. The stress is locked into the beverage container during manufacture and is often relieved as the lubricant materials contact the bottle. Lubricant materials appear to promote movement of the polyester molecules with respect to each other, relieving stress and leading to the creation of stress cracking. We have found that the degree of stress cracking is attributable, at least in part, to the amount of surface area of the bottle contacted by the lubricant. We have found in our experimentation that limiting the amount of surface area of the bottle that comes in contact with the lubricant can substantially improve the degree of stress cracking that occurs in the bottle material. Clearly, a substantial need exists to develop lubricating methods that result in the minimum amount of lubricant contact with the surface of the food container.
We have found that the problems inherent in conventional aqueous lubrication of conveyor systems used in food packaging and beverage bottling can be substantially improved using a continuous thin film lubricant layer formed on a conveyor surface. The lubricant layer is maintained at a thickness of less than about 3 millimeters, preferably about 0.0001 to 2 mm, with an add on of lubricant on the surface of less than about 0.05 gms-inxe2x88x922, preferably about 5xc3x9710xe2x88x924 to 0.02 gms-inxe2x88x922, most preferably about 2xc3x9710xe2x88x924 to 0.01 gms-inxe2x88x922. Such a thin lubricating film of the lubricant on the conveyor provides adequate lubrication to the conveyor system but ensures that the lubricant cannot foam, does not flow from the conveyor surface and contacts the absolute minimum surface area of the food container such as the beverage bottle as possible. Such a thin film lubricant maintains significant lubrication while avoiding waste of the lubricant composition and avoiding stress cracking promotion. We have found that the preferred mode of formation of the liquid lubricant compositions of the invention are in the form of an aqueous oil emulsion wherein the aqueous phase comprises about 10 to 50 wt % of the lubricant. The form of the emulsion can be either water in oil or oil in water emulsion. One preferred format of the emulsion is a phase unstable emulsion such that the emulsion separates forming an oil layer on top of a water layer which is then, in turn, contact with the conveyor surface. The methods of the invention can be used to convey virtually any food container on a conveyor line, but is particularly adapted to transporting both steel and aluminum cans and thermoplastic beverage containers such as polyethylene terephthalate beverage containers. Common PET beverage containers are formed with a pentaloid base having a five lobed structure in the base to provide stability to the bottle when it is placed on a surface. The contact with the lubricant on the pentaloid base must be minimized. We have found that using a thin film of emulsion lubricant, that less than about 10 to 300 mm2, preferably 20 to 200 mm2 of the surface of the bottle is contacted with lubricant. Certainly, the height of the lubricant in contact with the bottle is less than 3 millimeters. The motion of the conveyor, the tendency of the bottles to rock or move while being conveyed and the other aspects of relative movement at the bottle conveyor interface affect the height of the lubricant on the bottle. The methods of this invention are primarily directed to conveyor operations and do not involve any change in shape of the container arising from forming operations. The desirable coefficient of friction of the conveyor lubricant is about 0.1 to about 0.14.
The present invention provides in one aspect a container or conveyor for containers whose surface is coated at least in part with a thin, substantially non-dripping layer of a water-based cleaning agent-removable lubricant.
The invention also provides a process for lubricating a container, comprising applying to at least a part of the surface of the container a thin, substantially non-dripping layer of a water-based cleaning agent-removable lubricant.
The invention also provides a process for lubricating a conveyor system used to transport containers, comprising applying a thin, substantially non-dripping layer of a water-based cleaning agent-removable, substantially non-aqueous lubricant to a conveying surface of a conveyor, and then moving containers, such as beverage containers, on the conveyor.
The compositions used in the invention can be applied in relatively low amounts and with relatively low or no water content, to provide thin, substantially non-dripping lubricating films. In contrast to dilute aqueous lubricants, the lubricants of the invention provide drier lubrication of the conveyors and containers, a cleaner conveyor line and reduced lubricant usage, thereby reducing waste, cleanup and disposal problems.
Further features and advantages of the invention will become apparent from the detailed description that follows.